1. Field of the Invention
This invention relates to the field of wireless communication systems. More specifically, the present invention relates to power management by dynamically adjusting the transmission power of mobile stations based upon the quality of received signals by the base station.
2. Background
The use of wireless communication systems is growing with users now numbering well into the millions. One of the most popular wireless communications systems is the cordless telephone, consisting of a mobile unit (or handset) and a base station. Cordless telephones allow a user to talk over the telephone without having to remain in a fixed location. This allows users to, for example, move freely about a house while talking on the phone. However, one inconvenience associated with routine use of a cordless telephone is the constant need to recharge and replace depleted batteries in the handset.
As with any transmitted signal, the quality of the received signals varies based upon a number of factors, including atmospheric conditions, location of the mobile unit, or interference by walls or buildings. If a signal transmitted by the mobile unit has degraded, the base station may be unable to decode and process the signal. This may occur, for example, if the mobile unit is at the outer transmission boundary of the base station.
The power required by the mobile unit to transmit signals to the base station is one of the largest drains on battery power. In an attempt to extend battery life, mobile units are designed to vary the amount of transmission power based upon current needs. For example, a mobile unit located a long distance from the base station needs to transmit signals at a higher power level than a mobile unit near the base station. Current systems adjust the transmission power of the mobile unit based upon signal quality measurements taken over an extended period of time. Once the average signal quality diminishes below a set level, the mobile unit begins transmitting signals at a higher power level. After switching to the higher power level, the signal quality is again measured. If these signal quality measurements are above a threshold for an extended period of time, the base station instructs the mobile unit to switch to a lower power level to conserve battery power. While adjusting the transmission power levels of the mobile unit over extended periods of time has improved battery life, there is always a desire to further extend the useful life of the battery.
Improvements in battery technology, while helpful, have done little to avoid the seemingly ever-present need to recharge and replace mobile unit batteries. What is needed is a system to further conserve battery power by reducing the power consumed by the mobile unit.